1. ABOUT BSNL

On October 1, 2000 the Department of Telecom Operations, Government of India

became a corporation and was christened Bharat Sanchar Nigam Limited (BSNL).

Today, BSNL is the largest Public Sector Undertaking of India and its responsibilities

include improvement of the already impeccable quality of telecom services, expansion of

telecom network introduction of new telecom services in all villages and instilling

confidence among its customers.

At present the BSNL is the World’s Largest Seventh and India’s First

Telecommunication Company, with over 57.22 million customers as of December 2009

and the largest land line telephone provider in India.

Responsibilities that BSNL has managed to shoulder remarkably, definitely.

BSNL is the largest telecom operator in India and is known to everybody for Basic

Telephony Services for over 100 years. Presently the plain old, countrywide telephone

service is being provided through 32,000 electronic exchanges, 326 Digital Trunk

Automatic Exchanges(TAX), Digitalized Public Switched Telephone Network (PSTN) all

interlinked by over 2.4 lakhs km of Optical Fiber Cable, with a host of Phone Plus value

additions to our valued Customers. BSNL’s telephony network expands throughout the

vast expanses of the country reaching to the remotest part of the country.

Driven by the very best of telecom technology from chosen global leaders, it

connects each inch of the nation to the infinite corners of the globe, to enable you to step

into tomorrow.

Along with its vast customer base, BSNL’s financial and asset bases too are vast

and strong.

The telephone infrastructure along is worth about Rs. 1,00,000 crore (US $ 21.2

billion)

Turnover of Rs. 22,000 crore (US $ 4.6 billion)

BSNL is India’s oldest and largest Communication Service Provider (CSP).

Currently has a customer base of 90 million as of June 2008. It has footprints

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throughout India except for the metropolitan cities of Mumbai and New Delhi

which are managed by MTNL.

As on March 31, 2008 BSNL commanded a customer base of 31.55 million

Wireline, 4.58 million CDMA-WLL and 54.21 million GSM services.

Now from latest news BSNL records a net profit of Rs. 6,312 crore on revenues of

Rs.24,300 crore for the financial year 2001-02.

BSNL is working round the clock to take India into the future by providing world

class telecom services for the people of India.

1.1 Services provided by Bsnl

BSNL provides almost every telecom service in India. Following are the main

telecom services provided by BSNL

Universal Telecom Services: Fixed wireline services & Wireless in Local loop

(WLL) using CDMA Technology called bfone and Tarang respectively. As of December

31, 2007, BSNL has 81% marketshare of fixed lines.

Cellular Mobile Telephone Services: BSNL is major provider of Cellular Mobile

Telephone services using GSM platform under the brand name BSNL Mobile. As of Sep

30, 2009 BSNL has 12.45% share of mobile telephony in the country.

Internet: BSNL provides internet services through dial-up connection (Sancharnet) as

Prepaid, (NetOne) as Postpaid and ADSL broadband (BSNL Broadband). BSNL has

around 50% market share in broadband in India. BSNL has planned aggressive rollout in

broadband for current financial year.

Intelligent Network (IN): BSNL provides IN services like televoting, toll free calling,

premium calling etc.

3G: BSNL offers the '3G' or the'3rd Generation' services which includes facilities

like video calling etc.

IPTV: BSNL also offers the 'Internet Protocol Television' facility which enables us to

watch television through internet.

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FTTH: Fibre To The Home facility that offers a higher bandwidth for data

transfer.This idea was proposed on post-December 2009.

1.2 Bsnl Exchange

For smooth working of an exchange following unit are very important:-

1. Computer Unit: - it deals with additional services of the exchange to the customers

with the help of computers.

2. Power Plant:- to feed proper power supply to exchange

3. AC Plant: - to maintain the continuous temperature + or – 2 degree Celsius to the

digital switch (exchange).

4. MDF: - to connect switch (exchange) with the external environment (subscriber) i.e. it

is the interface between subscribers and exchange.

1.2.1 COMPUTER UNIT:

As the name specified it is the main part of the exchange that deals with the all services

provided by the exchange to the customers with the help of computer. It also provides the

updated data to all other part of the exchange.

The customers are using the services of the exchange by using the internet also

gets connected to the main server present this room via an internet room.

It mainly consists of the servers that are providing the different services. The main

servers of this room are:-

IVRS is used for the change number services provided by the exchange.

CERS are provided by the exchange to avoid the problems that the users are facing the

repairing of telephone. In this system when the user enters it’s complained it gets directly

entered to the server and user is allotted with an id number.

LOCAL DIRECTORY ENQUIRY is another services provided by the exchange, by

using this; subscribers calls the particular number and gets the directory enquiry. The

server present in the main computer room provides this service.

INTERNET DIRECTORY ENQUIRY is the latest service by the exchange. In this type

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of service makes it enquiry using the internet, which gets connected to the main server at

the internet room in the exchange and further to the main server in the computer room.

1.2.2 POWERPLANT:

As we know that, the power is the main source or any organization. It is the case

of E-10B exchange. That is the first requirement of any organization is the input.

The main source of this exchange is AC supply. However, as soon as the power

supply is gone off, then what is source? Even if the power supply gone off. Thus there

must be adjustment source of power.

The main parts of the power room are:

Batteries: - these are the instant sources of the power as soon as power is gone off.

UPS (Uninterrupted Power Supply):- the UPS must give supply to the computer. As we

know there is some equipment which can withstand any type of power supply, but there

are also some instruments which cannot withstand with this type of power supply, even a

microsecond delay will cause the loss of data.

Charging- Discharging Unit: - the batteries we are using in the power room need timely

charging. As soon as the AC power supply is on, we make use of the charging unit

present in the power room.

Inverter and Converter Unit: - the main use of this system is to change AC mains to

DC and vice versa as required by the parts of exchange.

Engine Room:-we know that the batteries are the instant source of supply but we cannot

use it for much larger time, thus for this, we have an engine to generate the power supply.

They are of 885 KVA. Thus, this room controls the supply of the engine.

1.2.3 CENTRAL AIR CONDITIONER:

For the function of electrical equipment, cooling system is basic requirement. The

basic advantages of cooling systems are following-

It provides the thermal stability so that the temperature does not reach the tolerance limit

of electronic equipment

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It saves equipment from dust so to avoid malfunction of equipment’s.

It protects equipment from excess humidity which can caused rusting of equipment.

1.2.4 MAIN DISTRIBUTION FRAME:

The primary function of MDF is: The fault of telephone number is removed in the

MDF; it is called as Fault Remove Section. These testing are T.T.Y. testing, Group

testing, etc. For any type of testing firstly we need the vertical no. or the live tester,

printer and computer test N.E. number of that particular telephone number. The telephone

numbers are also disconnected in the MDF because of some specific reason.

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2. INTRODUCTION TO COMMUNICATION SYSTEMS

The term communication system refers to the sending, receiving and processing of

information by electronic means. As such, it started with wire telegraphy in 1840’s

developing with the telephony some decades latter and radio at the beginning of the

twentieth century. Radio communication made possible by the invention of the triode

tube, which became more widely used and refined through the invention of transistor,

integrated circuit and the semiconductor devices. More recently the use of satellites and

fiber optics has made communication system more wide spread with an increasing

emphasis on computer and other data communication.

A modern communication system is first concerned with the sorting, processing

and storing of information before its transmission. The actual transmission then follows

with further processing and filtering of noise. Finally we have reception, which may

include processing steps as decoding, storage and interpretation. The various forms of

communication at present includes radio telephony, telegraphy, broadcasting point to

point and mobile communications, computer communications, radio telemetry, radar and

radio aids to navigation.

The invention of telephone in 1876 has marked revolution in world’s

telecommunication system. Soon it developed such that today, telephone network is far-

flung highly complex and highly integrated ‘system extending into almost every nook and

corner of all industrialized countries.

In earlier stages telephone switching was done manually. Modern switching is

effected automatically as on the Strowger, Crossbar and electronic system of

interconnection. These systems operate on the principle of common control with

incoming pulses temporarily stored in the device, which then controls the switches

directly or indirectly. In the recent past telephone dialing is done with out the aid of

operators. In this system switching mechanism selects the route to distant telephone and if

it finds the direct circuit busy, it explores in succession a number of alternate route and

establishes the connection over the least circuitous path.

Further progress in the transmission is in the direction of digital rather than analog

techniques. Speech signals will be multiplexed by the pulse methods with channels

interleaved in time instead of frequency. The most promising method is pcm, which

provides at the expense of bandwidth low vulnerability to interface and makes it possible

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to regenerate pulses perfectly at each repeater, so that there is no accumulator distortion

and hence no noise and cross talk.

In contrast to electro-mechanical switching system, electronic system will afford a

high degree of versatility through the program stored in the memory. Before long

facilities will be available to have features such as simplified codes for reaching

frequency called telephones subsequent automatic completion of calls to a busy specified

telephone, automatic centralized answering and like type.

More recently, communication satellite, employing microwave techniques are

increasingly used to handle several thousand voice channels with the advent of the

devices like traveling wave tube, the maser, the laser and the parametric amplifier optical

communication system are coming into vogue.

Electronic computers have been increasingly used to telecommunication links for

processing data collection, transmission and retrieval in private homes and in public

utility services. Indeed the future holds prospects of further advances in communication

techniques and acquires well to promote understanding and good will among men in

different parts of the world.

Telecommunication technologies have been undergoing rapid changes all over the

world and are becoming more intelligent due to developments in electronics. Many value-

added services have also proliferated in recent years. As a result, these developments like

large-scale integration and miniaturization of components have reduced power

consumption. Also, high-density assembly techniques have reduced the size and weight

of the equipment.

Two major changes in telecommunication technology, which have significantly

influenced the telecom infrastructure, are the introduction of Digital Signal Processing in

both switching, multiplexing and transmission of signals through fibre optic network. The

hardware technology used in switching transmission and thermal equipment has

undergone many changes since 1950 in India. In the switching area it has changed from

Strowger to Cross - Bar in 1960, to analog electronics in 1970’s, to hybrid of digital and

analog in 1980’s and now to digital electronics with higher level of emphasis on software

based control in recent design. Similarly transmission media on trunk routes has changed

from electrical to optical. The growing popularity of wireless transmission has resulted in

a major impact on the terminal equipment sector.

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2.1 Communication – Mobile

The central concept that made mobile communication as a usable commercial

proposition is the cellular principle. BELL Laboratories, US in 1970 first introduced

cellular principle Under cellular concept, the service area is divided into a number of

CLUSTERS, each cluster consists of a number of CELLS and each cell is assigned as

many CARRIERS as required by the traffic in that cell. There is a one-to-one

correspondence between the cells in each of the clusters that these cells use the same

carrier frequencies.

Figure 2.1: Mobile call setup

CELL:

A base station (transmitter) having a number of RF channels is called a cell. Each

cell covers a limited number of mobile subscribers within the cell

boundaries( Coverage area).Typical Cell Radius Aprrox = 30 Km(Start up), 1

KM (Mature)

2.2 Cellular Principal And Mobility Issues

 In mobile communication the wired 2W subscriber line is replaced with a wireless

mobile link. Once the customer is liberated from the confines of the wire and made free to

move, the following issues arise :-

Demand on the scarce radio resources.

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Authentication of the customer.

Security and privacy on the radio

Provide unique service profile.

Keep track of the user as they move.

Proving service across networks.

Billing the customer whenever and wherever he makes and receives calls from.

An important issue in mobile communication is the need to authenticate the

genuineness of the customer whenever he receives or attempts to make communication.

Since the media being open space, it is necessary to verify whether the customer is the

one whom he claims to be before resources allocation. Security of the mobile account is

to be ensured to prevent unauthorized use and also misuse of one’s subscription. Privacy

of the communication over radio is to be ensured though the radio signals are available

everywhere for interception.

One of the important issues for the customer is the availability of seamless service

profile irrespective of his location. This is an essential feature of the mobile

communication, particularly when the customer visits a service area served by an operator

different from his own. Different dialing codes for accessing the same service in different

networks can lay havoc in realizing the services by the customer.

Yet another challenging issue in mobile communication is the need to keep track

of the customer’s location so that an incoming call can be connected to him. Equally

important is the need to main established

Figure 2.2: A comparison of typical PSTN and mobile call scenarios is shown in figure.

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3. INTRODUCTION TO GSM

GSM is known as Global System for Mobile Communication. A technology

developed in 1985 by a French company known as Group Speciale Mobile.

Global System for Mobile (GSM) is a second generation cellular standard

developed to cater voice services and data delivery using digital modulation

Cellular radio provides mobile telephone service by employing a network of cell

sites distributed over a wide range. A cell site contains a radio transceiver and a base

station controller, which manages, sends, and receives traffic from the mobiles in its

geographical area to a cellular phone switch. It also employs a tower and its antennas, and

provides a link to the distant cellular switch called a mobile telecommunication switching

office. This MTSO places calls from land based telephones to the wireless customers,

switches calls between cells as mobile travel across cell boundaries, and authenticates

wireless customers before they make calls.

            GSM calls are either based on data or voice. Voice calls use audio codes called

half-rate, full-rate and enhanced full-rate. Data calls can turn the cell phone into a modem

operating at 9600 bps.

            It uses digital technology and time division multiple access transmission methods.

Voice is digitally encoded via a unique encoder, which emulates the characteristics of

human speech. This method of transmission permits a very efficient data rate/information

content ratio.

            One of its great strength is the international roaming capability that gives

consumers seamless and same standardized same number contact ability in more than 170

countries. GSM satellite roaming has extended service access to areas where terrestrial

coverage is not available.

GSM technology is continually evolving. Having made great leaps forward in the

past 10 years. It is facing an even greater evolution in the years ahead.

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3.1 HISTORY OF GSM

The first mobile telephone service started in 1946 in St. Louis, Missouri, USA as

an manually operated system. Between 1950 and 1960, it evolved as an automatic system

with reduced cost and increased, but small subscriber base.  Mobile telephony service in

its useful form appeared in 1960s. 

Table 3.1 Time history – milestones in the evolution of GSM

Yea

r

Event

198

2

Groupe Spécial Mobile established by the CEPT.

198

6

Reservation of the 900 MHz spectrum band for GSM agreed in the

EC Telecommunications Council. Trials of different digital radio

transmission schemes and different speech codes in several

countries.

198

7

Basic parameters of the GSM standard agreed in February.

198

8

Completion of first set of detailed GSM specifications for

infrastructure

198

9

Groupe Spéciale Mobile (transferred to an ETSI technical

committee) defines the GSM standard as the internationally

accepted digital cellular telephony standard

199

0

GSM adaptation work started for the DCS1800 band.

199

1

First GSM call made by Radiolinja in Finland.

199

2

First international roaming agreement signed between Telecom

Finland and Vodafone (UK).First SMS sent.

199

3

Telstra Australia becomes the first non-European operator.

Worlds first DCS1800 (later GSM1800) network opened in the UK.

199 GSM Phase 2 data/fax bearer services launched.

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4 GSM MoU membership surpasses 100 operators.

GSM subscribers hit one million.

199

5

117 GSM networks on air.

The number of GSM subscribers worldwide exceeds 10 million.

Fax, data and SMS services started, video over GSM

demonstrated.

The first North American PCS 1900 (now GSM 1900) network

opened.

199

6

First GSM networks in Russia and China go live.

Number of GSM subscribers hits 50 million.

199

7

First tri-band handsets launched.

199

8

Number of GSM subscribers worldwide over 100 million.

199

9

WAP trials begin in France and Italy.

200

0

First commercial GPRS services launched.

First GPRS handsets enter the market.

Five billion SMS messages sent in one month.

200

1

First 3GSM (W-CDMA) network goes live.

Number of GSM subscribers exceed 500 million worldwide.

200

3

First EDGE networks go live.

Membership of GSM Association breaks through 200-country

barrier.

Over half a billion handsets produced in a year.

200

8

GSM surpasses three billion customer threshold

.

The period from 1940 – 60

        The 1st mobile telephone service started in 1946 in St. Louis Missouri, USA.

        Between 1950 and 1960 it evolved as an automatic system.

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        Mobile telephony service in its useful from appeared in 1960s.

The period from 1980 - 95

Each country developed its own system

In 1982 the Conference of European Posts and Telegraphs (CEPT) formed a study

group called the Group Special Mobile (GSM) to study and develop a European

public land mobile system which had to meet certain criteria :

Good subjective speech quality.

Low terminal and service cost.

Support for international roaming

Ability to support hand held terminals.

Support for range of new service and facilities.             

Spectral efficiency.

In 1989, GSM responsibility was transferred to European Telecommunication Standards

Institute (ETSI)

GSM specifications were published in 1990 as:-

Carrier Separation - 200 kHz

Duplex Distance - 45 MHz

No. of RF Carriers - 124

Access Method - TDMA/FDMA

Modulation Method - GMSK

Transmission Rate - 270.833 Kbps

Speech Coding - Full rate 13 Kbps

Half rate 6.5 Kbps

Commercial service started in mid – 1991

 By 1993 there were 36 GSM networks in 22 countries

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The First Generation Mobile Communication System appeared in 1970s and remained

till 1980s.They used analog transmission techniques for radio link and confined its users

to their respective systems areas for which the mobile phone was designed. Capacity of

system was limited and roaming between the coverage areas of different systems was

impossible. Apart from being very expensive these system provides very poor QoS and

supported only voice communication. 

The Second Generation Mobile Communication System has grew out of the limitation

of first generation systems. They supported large subscriber base, carried both voice and

data and have capable of design and deliver new value added services. GSM and CDMA

emerged as the trend setting technologies. The domination of 2G systems became

apparent in second half of 1990s.

The Third Generation Mobile Communication Systems provide high functionality

with seamless global roaming. Apart from providing very high data rates, 3G systems

seek to integrate the wire line systems with mobile systems. 3G would provide users

consistent voice, data, graphical, multi-media regardless of their location in the network.

They also integrate the Intelligent Network (IN) capabilities into mobile systems.

3.2 OBJECTIVES OF GSM SYSTEM

 One of the important objectives of GSM group is to evolve a unified standard to

provide seamless roaming.Another landmark decision taken by the group is to standardize

a digital radio interface for the communication between the mobile handset and the radio

transmitter / receiver. The design objectives of the GSM system can be briefly states as

below:

Excellent speech quality

High security and privacy

Low module terminal cost

Low service and facilities cost

Design of sleek and handled mobile terminals

International roaming

Wide range of services and facilities

Ability to adopt to new and innovative features

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Narrowband ISDN compatibility

Digital Radio

High Spectral efficiency

 The digital radio uses the 900/1800 MHz  band.  The mobile terminal vary in power

class 20 watts to as low as 0.8 watts.  A GSM cell can cover a maximum distance of up to

30 Kms.  The system can provide service to mobile customers traveling up to a maximum

speed of 250 Km/hr.

3.3 Characteristics of GSM Standard

• Fully digital system using 900,1800 MHz frequency band.

• TDMA over radio carriers(200 KHz carrier spacing.

• 8 full rate or 16 half rate TDMA channels per carrier.

• User/terminal authentication for fraud control.

• Encryption of speech and data transmission over the radio path.

• Full international roaming capability.

• Low speed data services (upto 9.6 Kb/s).

• Compatibility with ISDN.

• Support of Short Message Service (SMS)

4. SERVICES PROVIDED BY GSM

Services are defined as anything the end user explicitly sees as worth paying for.

The primary objective of a mobile telephony system is to allow mobile subscribers to

communicate effectively.

Telecommunication services can be divided into

Tele-services

Bearer or Data Services

Supplementary services

4.1 TELE SERVICES:

The most basic teleservice supported by GSM is telephony. As with all other

communications, speech is digitally encoded and transmitted through the GSM network

as a digital stream. There is also an emergency service, where the nearest emergency-

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service provider is notified by dialing three digits no. similar to 911,112. It provides

Dual Tone Multi Frequency(DTMF), a tone signaling facility which is often used for

various control purposes, such as remote control of answering machines and interacting

with automated telephone services.

4.2 BEARER SERVICES:

A variety of data services is offered. GSM users can send and receive data, at

rates up to 9600 bps, to users on POTS (Plain Old Telephone Service), ISDN, Packet

Switched Public Data Networks, and Circuit Switched Public Data Networks using a

variety of access methods and protocols, such as X.25 or X.32. Since GSM is a digital

network, a modem is not required between the user and GSM network, although an audio

modem is required inside the GSM network to interwork with POTS.

A unique feature of GSM, not found in older analog systems, is the Short Message

Service (SMS). SMS is a bi-directional service for short alphanumeric (up to 160 bytes)

messages. Messages are transported in a store-and-forward fashion. For point-to-point

SMS, a message can be sent to another subscriber to the service, and an

acknowledgement of receipt is provided to the sender. A further variation of the SMS is

the cell broadcast service TS23, SMSCB(SMS Cell Broadcast).SMSCB messages are

broadcast only in a limited region of the network. A text message with a maximum length

of 93 characters can be broadcast to all mobiles within a certain geographic area, for

sending messages such as traffic updates or news updates. Messages can also be stored in

the SIM card for later retrieval.

EMS is an extension of SMS. SMS was limited to text messages only. However,

as ring tones and pictures gained a lot of popularity, EMS was introduced. EMS was

developed by major GSM manufacturers as an open 3GPP standard. It allows unicolor

pictures with 16 × 16 or 32 × 32 pixels to be sent and the pictures to be modified in the

handset.

MMS is similar to SMS or EMS, however has much higher

capabilities in terms of size and flexibility. The MMS standard was

developed by a consortium of industry partners and has become a

3GPP standard. In addition to pure text, MMS is capable of transmitting

pictures, melodies and multimedia sequences of different kinds. MMS

can transmit up to 100 kbyte of data and can handle AMR-coded

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speech, pictures (e.g. JPEG or GIF), music and even video. From the

network point of view, a MMS-Center, called MMS-C, is required, which

is responsible for storing, converting and forwarding MMS data.

A comparison between SMS, EMS and MMS is provided in Table.

Table4.1 comparison between SMS,EMS,MMS

Another service called Voice mail is provided.This service is an answering

machine within the network that is controlled by the subscriber. The subscriber accesses

the mail box using a personal security code.

Other bearer services include, Unified Messaging Services(UMS), Group 3 fax,

Electronic mail.

4.3 SUPPLEMENTARY SERVICES:

Call related services : Supplementary services are provided on top of teleservices or

bearer services. In the current (Phase I) specifications, they include several forms

• 4.3.1 Call Forwarding- Calls can be sent to various numbers defined by the user

in the following situations:

Call forwarding on MS not reachable

Call forwarding on MS busy

Call forwarding on no reply

Call forwarding, unconditional

• 4.3.2 Call Barring:

Barring of outgoing calls: The subscriber can activate or deactivate this

service from the MS with a variety of options for barring outgoing calls.

• Bar all outgoing calls

• Bar all outgoing international calls

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• Bar all outgoing international calls except those directed to the

home PLMN.

Barring of incoming calls: This is desirable because in some cases the

called mobile subscriber is charged for parts of an incoming call (during

international roaming)

• Barring of all incoming calls

• Barring of incoming calls when outside home PLMN

• 4.3.3 Call Hold: This supplementary service enables the subscribers to put the

basic normal telephony service on hold in order to set up a new call or accept a

waiting call

Many additional supplementary services will be provided in the Phase 2 specifications,

such as

• 4.3.4 Multi Party Call Conferencing - Link multiple calls together

• 4.3.5 Call Waiting- This service notifies the mobile subscriber, usually by an

audible tone, for incoming call. The incoming call can be any type of basic service

including speech, data or fax. There is no notification in the case of an emergency

call or SMS. To activate call waiting dial *43#.

• 4.3.6 Call line identification service- These cover both the presentation and

restriction of the calling line identity

CLIP – Caller line identification presentation: The presentation part of the

service supplies the called party with the ISDN or MSISDN number of the

calling party.

CLIR – Caller line identification restriction: The restriction service

enables calling parties to restrict the presentation of their number on the

MSs of called parties.

• 4.3.7 CUG – Closed user group: The CUG service enables subscriber connected

to the PLMN/ISDN and possibly other networks, to form groups in which access

is restricted. Example: members of a specific CUG can communicate with each

other, but generally not with users outside the group.

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4.4 INNOVATIVE FEATURES

4.4.1 Regional and local subscription:

These features allow subscribers to subscribe to a service in a specified

geographical area.Requests for service outside the area are rejected with the exception

of emergency calls and SMS. For local subscriptions, the geographical area consists

of a number of cells, and for regional subscription, the area consists of LAs.

4.4.2 Value Added Services:

The value added services include:

• Mobile Messaging

• Mobile internet

• Mobile intelligent Network Services

Mobile Messaging

• Short Message Services (SMS): The service allows simple text message

consisting of a maximum of 160 alphanumeric characters to be sent to or from

an MS. If the MS is switched off, or has left the coverage area, the message is

stores in a Short Message Service Center (SMS-C). When the mobile is

switched on again or has re-entered the network coverage area, the subscriber

is informed that there is a message.

• Enhanced Messaging System (EMS): EMS can support relatively simple

pictures,sounds and animation. EMS messages that are sent to devices that do

not support it will be displayed as SMS transmissions.It is a 3GPP standard.

• Multimedia Message Service(MMS): MMS means a multimedia

presentation which consists of music, voice, image, text, video and graphics

all synchronized across a common timeline. Eg: “Synchronized Power Point

Presentations”. MMS-enabled mobile phones enable subscribers to compose

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and send messages with one or more multimedia parts. Mobile phones with

built-in or attached cameras, or with built-in MP3 players are very likely to

also have an MMS messaging client -- a software program that interacts with

the mobile subscriber to compose, address, send, receive, and view MMS

messages.A comparison between SMS and MMS in given the below table.

SMS MMS

• Text Based Messaging• rich content including text, graphic,

photos etc.

• Proprietary Standard• Based upon 3GPP & WAP

standards.

• Store & Forward system • Store & Forward system

• Uses signaling links • MMS uses main data channel.

Table 4.2 comparison between SMS and MMS

• Instant Messaging: It enables to communicate with another individual in real

time, analogous to a telephone conversation but using text based

communication instead of voice-based communication.

• Streaming: It enables real time or on demand distribution of audio, video and

multimedia on the internet. It is simultaneous transfer of digital media (video,

voice and data) so that it is received as a continuous real-time stream.

4.4.3 Mobile Applications

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Figure 4.3: Mobile applications

4.4.4 Location Based Applications

In this age of significant telecommunications competition, mobile network

operators continuously seek new and innovative ways to create differentiation and

increase profits. One of the best ways to do accomplish this is through the delivery of

highly personalized services. One of the most powerful ways to personalize mobile

services is based on location.

Services Segments:

• Safety

Emergency Dispatch

Child/Family tracking

Auto theft tracking

Roadside assistance

• Community

21

Friend Finder

Dating

Chatting

• Personal Lifestyles

Entertainment & Fun

Finding & Guiding

Information services

• Tracking

Fleet Management

Vehicle dispatch

Rental car tracking

Remote workforce management

Positioning: One of the most obvious technologies behind LBS is positioning, with the

most widely recognized system being the Global Positioning System (GPS). There are

however, other means of positioning in addition to GPS. These other technologies are

network based positioning and typically rely on various means of triangulation of the

signal from cell sites serving a mobile phone. In addition, the serving cell site can be used

as a fix for location of the user.

Geographic Information Systems: Geographic data is an important aspect of any

location system. Geographic Information Systems (GIS) provide the tools to provision

and administer base map data such as man made structures (streets, buildings) and terrain

(mountains, rivers). GIS is also used to manage point-of-interest data such as location of

gas stations, restaurants, nightclubs, etc. Finally, GIS information also includes

information about the radio frequency characteristics of the mobile network. This allows

the system to determine the serving cell site of the user.

4.4.5 Machine to Machine communication (M2M)

Some key technologies for M2M

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• Bluetooth

• GSM/GPRS

• GSM/SMS

• WiFi

4.4.6 Push-To-Talk (PTT)

Push-To-Talk (PTT) is a two-way communication service that works like a

"walkie talkie".A normal cell phone call is full-duplex, meaning both parties can hear

each other at the same time. PTT is half-duplex, meaning communication can only travel

in one direction at any given moment.

To control which person can speak and be heard, PTT requires the person

speaking to press a button while talking and then release it when they are done. The

listener then presses their button to respond. This way the system knows which direction

the signal should be traveling in.

4.4.7 Push-To-Talk over cellular (PoC)

The Motorola, Nokia, Ericsson, Siemens, Huawei, Mobile Tornado, Wireless ZT, etc.

versions of PTT are based on 2.5G or 3G packet-switched networks and use SIP and RTP

protocols. These particular versions of PTT are called "Push to Talk over Cellular", which

is abbreviated "PoC"

5. GSM Operation

23

Figure 5.1: Block diagram of Gsm Opeartion

5.1 Speech Coding -Done at Transcoder of BSC and MS

- The Linear Predictive Coder uses RPE-LTP(Regular Pulse Excitation- Long

Term Prediction)

- Converts 64kbps voice to 13kbps(260 bits every 20ms)

- Source coding reduces redundancy in the speech signal and thus results in signal

compression,which means that a significantly lower bit rate is achieved than

needed by the originalspeech signal. The speech coder/decoder is the central part

of the GSM speech processingfunction, both at the transmitter (Figure 4.25) as

well as at the receiver (Figure 4.26). Thefunctions of the GSM speech coder and

decoder are usually combined in one building blockcalled the codec

(COder/DECoder).

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5.2 Channel Coding - Done at BTS and MS

- The Different methods of channel coding used in GSM are,

• Block coding

• Convolutional coding

Block coding:

When the block coding is used, one or several check bits are added to the

information block. The check bits only depend on the bits in that every block. A

simple form of block coding is using is parity coding. Block coding is mainly used

for detecting errors.

Convolutional coding:

The Convolutional coder consists of a shift register into which the

information bits are shifted one by one. Convolutional coding is not only good for

detecting errors, but also for correcting them.

5.3 Bit Interleaving - Done at BTS and MS

- In GSM the channel coder produces a total of 456 bits for every 20 ms segment

of speech.These are in blocks of 57 bits interleaved over the burst.

- The interleaving approach is to distribute codewords from the convolutional

encoder byspreading in time and merging them across several bursts for

transmission.By time spreading, each of the codewords is distributed across a

threefold length. Merging the bit sequences generated in this way has the effect

that the individual bits from each of the three codewords are sorted into alternate

bursts; this way each codeword is transmitted as distributed over a total of three

bursts, and two bits of a data block are never transmitted adjacent to each other.

5.4 Ciphering - Done at BTS and MS

– EX OR data with cipher block, which is generated by applying A5 Algorithm to

the Ciphering Key(Kc) The security function that ciphers the information sent and

received by the MS required the cipher key Kc. The generation of the Kc is based

on the crypto graphical algorithms A8, and the Ki. Also A8 is located on the SIM.

Ciphering start procedure :

This ciphering start procedure is initiated from the MSC/VLR by sending the

message a cipher mode command the Kc. The Kc will be removed form the

message by the BTS before sending it on to the MS, so that the Kc will be never

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be sent on the air. When the MS receives this message it will be send the message

cipher mode complete in the cipher mode using the calculated Kc stored on the

SIM card. If the BTS can decipher this message it will be inform the MSC/VLR

that ciphering has started.

5.5 Multiplexing - Done at BTS

5.6 Modulation - Done at BTS and MS

– GMSK(Gaussian filtered Minimum Shift Keying)

– Phase change of +90 for 0 and -90 for 1

The operation of the GSM system can be understood by studying the sequence of events

that takes place when a call is initiated from the Mobile Station.

5.7 Call from Mobile Phone to PSTN:

When a mobile subscriber makes a call to a PSTN telephone subscriber, the following

sequence of events takes place:

1. The MSC/VLR receives the message of a call request.

2. The MSC/VLR checks if the mobile station is authorized to access the network. If

so, the mobile station is activated. If the mobile station is not authorized, service

will be denied.

3. MSC/VLR analyzes the number and initiates a call setup with the PSTN.

4. MSC/VLR asks the corresponding BSC to allocate a traffic channel (a radio

channel and a time slot).

5. The BSC allocates the traffic channel and passes the information to the mobile

station.

6. The called party answers the call and the conversation takes place.

7. The mobile station keeps on taking measurements of the radio channels in the

present cell and neighboring cells and passes the information to the BSC. The

BSC decides if handover is required, if so, a new traffic channel is allocated to the

mobile station and the handover is performed. If handover is not required, the

mobile station continues to transmit in the same frequency.

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5.8 Call from PSTN to Mobile Phone:

When a PSTN subscriber calls a mobile station, the sequence of events is as follows:

1. The Gateway MSC receives the call and queries the HLR for the information

needed to route the call to the serving MSC/VLR.

2. The GMSC routes the call to the MSC/VLR.

3. The MSC checks the VLR for the location area of the MS.

4. The MSC contacts the MS via the BSC through a broadcast message, that is,

through a paging request.

5. The MS responds to the page request.

6. The BSC allocates a traffic channel and sends a message to the MS to tune to the

channel. The MS generates a ringing signal and, after the subscriber answers, the

speech connection is established.

7. Handover, if required, takes place, as discussed in the earlier case.

The MS codes the speech at 13 Kbps for transmission over the radio channel in the given

time slot. The BSC converts (or transcodes) the speech to 64 Kbps and sends it over a

land link or radio link to the MSC. The MSC then forwards the speech data to the PSTN.

In the reverse direction, the speech is received at 64 Kbps rate at the BSC and the BSC

does the transcoding to 13 Kbps for radio transmission.

In its original form, GSM supports 9.6 Kbps data, which can be transmitted in one TDMA

time slot. Over the last few years, many enhancements were done to the GSM standards

(GSM Phase 2 and GSM Phase 2+) to provide higher data rates for data applications.

6. GSM NETWORK ARCHITECTURE

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Figure 6.1: Block diagram of GSM Architecture

6.1 GSM NETWORK STRUCTURE

Every telephone network needs a well designed structure in order to route

incoming called to the correct exchange and finally to the called subscriber. In a mobile

network, this structure is of great importance because of the mobility of all its subscribers.

In GSM system, network is divided into following partitioned areas:-

6.1.1 GSM service area :- It is the total area served by the combination of all member

countries where a mobile can be serviced. The more operators who sign contracts

agreeing to work together, the more this area will increase.

6.1.2 PLMN service area :- 

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Figure 6.2: PLMN service area

Based on its size these can be several within a country. All incoming calls for a

GSM/PLMN network will be routed to a gateway MSC which works as an incoming

transit exchange. The gateway MSC consists the inter working functions to make these

connections.

6.1.3 MSC service area :- 

Figure 6.3: MSC service area

There can be several MSC/VLR in one PLMN.To route a call to a mobile subscriber, the

path through links to MSC in the MSC area where the subscriber is currently located. The

mobile location can be uniquely identified since the MS is registered in a VLR, which is

generally associated with an MSC.

 6.1.4 Location areas :- LA’s are several within a MSC/VLR combination. A LA is a part

of the MSC/VLR service area in which a MS may move freely without updating location

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information to the MSC/VLR exchange that control the LA. In a LA a paging message is

broadcast to find the called mobile subscriber. LA can be identified by using the location

area identity. LA is used to search for the subscriber in an active state.

 6.1.5 Cells :- Location area subdivided into a number of cells. A cell is the geographical

area covered by one Base Transceiver Station. A cell is the smallest geographical entity

in a PLMN.A cell could be any size, from a radius of tens of kilometers down to a radius

of tens or hundreds of meters.

Figure 6.4: Cells in Location Area

It is an identity served by one BTS. The MS differentiate between cells using BSIC

(Base Station Identification Code) that the cell site broadcast over the air.

6.2 MOBILE STATION

The mobile station (MS) includes radio equipment and the man machine interface

that a subscriber needs in order to access the service provided by the GSM PLMN. The

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MS may include provisions for the data communication as well as voice. A mobile

transmits and receives message to and from the GSM system over the air interface to

establish and continue connections through the system.

Each MS is identified by an IMEI that is permanently stored in a mobile unit.

Upon request, the MS sends this number over he signaling channel to the MSC. The IMEI

can be used to identify mobile units that are reported stolen or operating incorrectly.

The mobile subscriber ISDN number (MS ISDN) is the number that the calling

party dials in order to reach the subscriber. It is used by the land network to route calls

towards an appropriate MSC. The international mobile subscriber identity (IMSI) is

permanently assigned to him. Temporary mobile subscriber identity (TMSI) is also

assigned by the GSM system which can be periodically changed and protect the

subscriber from being identified by those attempting to monitor the radio channel.

6.2.1 FUNCTIONS OF MOBILE STATION

        The primary functions of MS are to transmit and receive voice and data over the

Air interface of the GSM system. MS performs the signal processing function of

digiting, encoding, error protecting, encrypting, and modulating the transmitted

signals. It also performs the inverse functions on the received signals from BS.

In order to transmit voice and data signals, the mobile must be in synchronization

with the system.

To achieve this, the MS automatically tunes and synchronizes to the frequency

and TDMA timeslot specified by the BSC.

The MS monitors the power level and signal quality, determined by the BER for

known receiver bit sequences from both its current BTS and up to six surrounding

BTSs. This data is received on the downlink broadcast control channel. The

system then uses this list for best cell handover decisions.

MS keeps the GSM network informed of its location during both national and

international roaming, even when it is inactive.

MS includes an equalizer that compensates for multi path distortion on the

received signal

The MS can store and display short received alphanumeric messages on the LCD.

These messages are limited to 160 characters in length.

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6.2.2 SIM CARD

GSM subscribers are provided with a sim card with its unique identification at the

very beginning of the service. The suscriber is identified in the system when he inserts the

SIM card in the mobile equipment. The smart card SIM is potable between Mobile

equipment (MS) units. The user only needs to take his smart card on a trip because it can

be used in any GSM specified mobile set. He can then a ME unit at the destination, even

in the another country, and insert his own SIM. Also, the GSM system will be able to

reach him at the ME unit he is currently  using.

The SIM is a removable card, containing an integrated circuit chip with a

microprocessor, random access memory (RAM), and read only memory (ROM). The

subscriber inserts it in the MS unit when he or she wants to use the MS to make or receive

a call.

6.2.3 INTERNATIONAL MOBILE SUBSCRIBER IDENTITY

An IMSI assigned to each authorized GSM user. It consists of a mobile country

code (MSC), mobile network code (MNC), and a PLMN unique mobile subscriber

identification number (MSIN). The IMSI is not hardware-specific. Instead, it is

maintained on a SC by an authorized  subscriber and is only absolute identify that a

subscriber has within the GSM system.

6.2.4 TEMPORARY  MOBILE SUBSCRIBER  IDENTITY

A TMSI is a MSC-VLR specific alias that is designed to maintain user

confidentiality. It is assigned only after successful subscriber authentication.  The

correlation of a TMSI to an IMSI only occurs during a mobile subscriber’s initial

transaction with an MSC (for example, location updating). Under certain conditions (such

as traffics system disruption and malfunctioning of the system), the MSC can direct

individual TMSIs to provide the MCS with their IMSI.

6.2.5 THE MOBILE STATION ROAMING NUMBER (MSRN)

The MSRN is allocated on temporary basis when the MS roams into another

numbering area. The MSRN number is used by the HLR for rerouting calls to the MS. It

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is assigned upon demand by the HLR on a per-call basis. The MSRN for PSTN/ISDN

routing shall have the same structure as international ISDN numbers in the area in which

the MSRN is allocated. The HLR knows in what MSC/VLR service area the subscriber is

located. At the reception of the MSRN, HLR sends it to the GMSC, which can now route

the call to the MSC/VLR exchange where the called subscriber is currently registered.

6.3 RADIO SUB SYSTEM (RSS)

Figure 6.5: Block diagram Radio/Base sub system

BASE STATION SYSTEM (BSS)

The BSS is a set of BS equipment (such as transceivers and controllers) that is the

entry responsible for communication with Mobile Stations in a certain area. A BSS may

consist of one or more BS. The BSS includes two types of machines: - 

The BTS in contact with the MSs through the radio interface.

The BSC the latter being in contact with the MSC.

6.3.1 BTS

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A BTS compares radio transmissions and reception devices, up to and including

the antennas, and also all the signal process specific to the radio interface.

A BTS is a network component that serves one cell and is controlled by a BSC. A

BTS is typically able to handle 3 to 5 radio carriers, carrying between 24 and 40

simultaneous communications.

An important component of the BSS that is considered in the GSM architecture as

a part of the BTS is the Trans coder/Rate Adapter Unit (TRAU). The TRAU is the

equipment in which coding and decoding is carried out as well as rate adoption in case of

data. Although the specifications consider the TRAU as a subpart of the BTS, it can be

sited away from the BTS (at MSC), and even between the BSC and the MSC.

Functions of BTS

The primary responsibility of BTS is to transmit and receive radio signals from a

mobile over as air interface. To perform this function completely the signals are

encoded, encrypted, multiplexed, modulated and then fed to the antenna system at

the cell site. Transcoding to bring 13-kbps speech to a standard data rate of

16kbps and then combining four of these signals to 64 kbps is essentially a part of

BTS.

The received signals from the mobile is decoded, decrypted, and equalized for

channel impairments.

Random access detection is made by BTS, which then sends the messages to BSC.

The channel subsequent assignment is made by BSC.

6.3.2 BSC

BTS to notify the MS to advance the timing such that proper synchronization

takes place The BSC is connected to the MSC on one side and to the BTS on the other.

The BSC performs the Radio Resource (RR) Management for the cells under its control.

It assigns and release frequencies and timeslots for all MSs in its own area. It also

reallocates frequencies to the BTSs in its area to meet locally heavy demands during peak

hours or on special events. The BSC controls the power transmission of both BSSs and

MSs in its area. The minimum power level for a mobile unit is broadcast over the BCCH.

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The BSC provides the time and frequency synchronization reference signals broadcast by

its BTSs. The BSC also measures the time delay of received MS is not centered in its

assigned timeslot at the BTS, the BSC can direct the.

Functions of BSC

The BSC also performs traffic concentration to reduce the number of transmission

lines from the BSC to its BTSs, as discussed in the last section.

MSC-BSS Configurations:

Figure 6.6: MSC-BSS configuraion

6.4 SWITCHING SUBSYSTEMS

NETWORK SWITCHING SUBSYSTEM (NSS):

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Figure 6.7: Block diagram of Network Swithing Subsystem

6.4.1 MOBILE SWITCHING CENTRE AND GATEWAY SWITCHING CENTRE

The network and the switching subsystem together include the main switching

functions of the GSM as well as the databases needed for the subscriber data and the

mobility management (VLR). The main role of the MSC is to manage the communication

between the GSM users and other telecommunication network users. The basic switching

functions are performed by the MSC whose main function is to coordinate setting up calls

to and from GSM users. The MSC has interface with the BSS on the one side and the

external networks on the other. The main difference between MSC and EXCHANGE in a

fixed network is that the MSC has to take into account the impact of the allocation of RRs

and the mobile nature of subscribers and has to perform.

6.4.2 VARIABLE LOCATION REGISTER

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The VLR is collocated with an MSC. A MS roaming in an MSC area is controlled

by the VLR responsible for that area. When a MS appears in a LA it starts a registration

procedure. The MSC for that area notices this registration and transfers to the VLT, the

identity of the LA where the MS is situated. A VLR may be in charge of one or several

MSCs LA’s. the VLR constitutes the databases that support the MSc in the storage and

retrieval of the data of subscribers present in that area. When an MS enters the MSCs area

borders, it signals its arrival to the MSC that stores its identity in the VLR. The

information necessary to manage the MS is contained in HLR and is transferred to the

VLR so that they can be easily retrieved if so required. PLMN may contain VLR.

6.4.3 HOME LOCATION REGISTER

HLR is a database that permanently stores data related to a given set of

subscribers.

Various identification numbers and addresses as well as authentication

parameters, services, special routing information are stored.

Current subscriber status including a subscriber’s temporary roaming number and

associated VLR if the mobile is roaming are maintained.

HLR is responsible for storage and provision of SIM authentication and

encryption parameters form the AUC.

one or several HLRs.

6.4.4 AUTHENTICATION CENTER

The AUC stores information that is necessary to protect communication through

the air interface against intrusions, to which the mobile is vulnerable.

The legitimacy of the subscriber is established through authentication and

ciphering, which protects the user information against unwanted disclosure.

Authentication information and ciphering keys are stored in a database within the

AUC which protects the user information against unwanted disclosure and access.

6.4.5 EQUIPMENT IDENTIFY REGISTER

EIR is a database that stores the IMEI numbers for all registered ME units. The IMEI

uniquely identifies all registered ME. There is generally one EIR per PLMN. It interfaces

to the various HLR in the PLMN. The EIR keeps track of all ME units in the PLMN. It

maintains various lists of message. The database stores the ME identification and has

37

nothing do with subscriber who is receiving or originating call. There are three classes of

ME that are stored in the database, and each group has different characteristics.

White List: contains those IMEIs that are known to have been assigned to valid

MS’s. This is the category of genuine equipment.

Black List: contains IMEIs of mobiles that have been reported stolen.

Gray List: contains IMEIs of mobiles that have problems (for example, faulty

software, wrong make of the equipment). This list contains all MEs with faults not

important enough for barring.

6.4.6 INTERWORKING FUNCTION

GSM provided a wide range of data services to its subscribers. The GSM system

interface with the various forms of public and private data network currently available. It

is the job of the IWF to provide this interfacing capability. 

The IWF, which is essence is a part of  MSC, provides the subscriber with access

to data rate and protocol conversion facilities so that data can be transmitted between

GSM Data Terminal Equipment (DTE) and a land-line DTE 

6.4.7 ECHO CANCELER 

EC is use on the PSTN side of the MSC for all voice circuits. The EC is required

at the MSC PSTN interface to reduce the effect of GSM delay when the mobile is

connected to the PSTN circuit. The total round-trip delay introduced by the GSM system,

which is the result of speech encoding, decoding and signal processing is of the order of

180 ms. The standard echo canceller cancels about 70 ms of delay.

  As the GSM round-trip delay added and without the EC the effect would be

irritating to the MS subscriber.

Functions of MSC

As stated, the main function of the MSC is to coordinate the set up of calls

between GSM mobile and PSTN users. Specifically, it performs functions such as

paging, resource allocation, location registration, and encryption.

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The MSC is a telephony switch that performs all the switching functions for MSs

located in a geographical area as the MSC area. The MSC must also handle

different types of numbers and identities are used in the fixed part of the network,

such as, for routing.

The call-handling function of paging is controlled bt MSC. MSC coordinates the

set up of paging is controlled in different registers: IMSI, TMSI, ISDN number

and MSRN. In general identities are used in  the interface between the MSC and

the MS, while numbers are used in the fixed part of the nrtwork, such as, for

routing.

The call-handling function of the paging is controlled by MSC. MSC coordinates

the set up of call to and from all GSM subscribers operating in its areas. The

dynamics allocation of access resources is done in coordination with the BSS.

More specifically, the MSC decides when and which types of channels should be

assigned to which MS. The channel identity and related radio parameters are the

responsibility of the BSS; The MSC provides the control for the subscriber

authentication procedure.

The MSC supervises the connection transfer between different BSSs for MSs,

with an active call, moving from one call to another. This is ensured if the two

BSSs are connected to the same MSC but alsowhen they are not. In this later case

the procedure s more complex, since more than one MSC is involved.

The MSC performs billing on calls for all subscribers based in its areas. When the

subscriber is in roaming elsewhere, the MSC obtains data for the call billing from

the visited MSC.

Encryption parameters transfers from VLR to BSS to facilitate ciphering on the

radio interface are done by MSC. The exchange of signaling information on the

various interface toward the other network elements and the management of the

interfaces themselves are all controlled by the MSC.

The MSC serves as a SMS gateway to forward SMS messages from Short

Message Service Centers (SMSC) to the subscribers and from the subscribers to

the SMSCs. It thus acts as a message mailbox and delivery system.

6.5 OPERATION AND MAINTENANCE SUBSYSTEM (OMS):

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OMS is used to configure, control and monitor the GSM network.  It

comprises of two parts:

Operation and Maintenance Centre - Switch

Operation and Maintenance Centre - Radio

While OMC-S is used in conjunction with the NSS, OMCs-R is used in conunction

with the BSS.  The OMC-R controls the traffic load on the various cells and performs

automatic reconfiguration of the transceivers to cope with the fluctuation of traffic, load

caused due to the mobility of the customers.

The OMCs also provide traffic data measurements, reporting and analysis.  OMCs

also store all the data and software for the network elements and perform as the central

maintenance control point for all the network elements.

6.6 ENHANCED SERVICES SUBSYSTEM (ESS):

The ESS includes such elements as Unified Messaging System (UMS), Wireless

Application Protocol (WAP) System, Interlligent Network (IN) system, Content and

Location Based Services (C&LBS) system etc.

The Unified Messaging System provides a variety of voice and data services such as:

Voice Mail

Fax Mail

E-Mail

Visual Mail

Short Message Service (SMS)

All the above services can be subscribed by the customer and can be provided from a

single platform.

The WAP system allows wireless access to Internet sites that are enabled for

customized access from mobile handsets.  Thus a customer, on move, can surf the web

from his WAP enabled handset through the WAP gateway.  The WAP system also

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manages telephony events such as incoming call etc when a subscriber connected to the

Internet.

Intelligent Network system provides a host of value added features and services such as:

Pre-paid service (PPS)

Free Phone Service (FPH)

Premium Rate Services (PRM)

Mobile Virtual Private Network (MVPN)

Universal Access Number (UAN) etc

The pre-paid service provided through IN system in conjunction with Voucher

Management System (VMS) and Over-the-Air Charging (OTAC) system can provide

national and international roaming and recharging through a variety of payment

instruments such as Credit/Debit card, ECS etc.  It can also support a number of tariff and

promotional plans that can be chosen by the customer himself/herself.

Content and Location Based Services can offer a variety of PUSH and PULL

services ranging from advising the customer of the discounts being offered in the shops

near his current ‘location’ to verification of flight details etc.

6.7 BILLING AND CUSTOMER CARE SYSTEM (B&CCS):

Billing and Customer Care System is responsible for obtaining the call details of

each of the customers from the HPLMN as well as from all the VPLMNs for raising the

invoice.  B&CCS incorporates a powerful and flexible rating engine that would enable the

service provider to offer innovative and competitive tariff packages.

The Customer Care module includes an automatic Service Provisioning Module

that will activate / deactivate a customer account from a Customer Care terminal without

the need for any manual intervention.  The CC module also would handle the Trouble

Tickets generated on faults reported by the customer and routes such tickets automatically

to appropriate terminal for action.

The B&CCS also incorporates a sophisticated Printing Subsystem for distributed

printing of the customer invoices.

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7. OVER VIEW OF THE GSM INTERFACE

The communication relationships between the GSM network

components are formally described by a number of standardized

interfaces.

Figure 7.1: GSM Interface

The A interface between BSS and MSC is used for the transfer of data

for BSS

management, for connection control and for mobility

management.Within the BSS, the Abis interface between BTS and BSC

and the air interface Um have been defined.

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An MSC which needs to obtain data about an MS staying in its

administrative area,

requests the data from the VLR responsible for this area over the B

interface. Conversely, the MSC forwards to this VLR any data generated

at location updates by MSs. If the subscriber reconfigures special

service features or activates supplementary services, the VLR is also

informed first, which then updates the HLR. This updating of the HLR

occurs through the D interface. The D interface is used for the

exchange of location-dependent subscriber data and for subscriber

management. The VLR informs the HLR about the current location of

the mobile subscriber and reports the current MSRN. The HLR transfers

all of the subscriber data to the VLR that is needed to give the

subscriber their usual customized service access. The HLR is also

responsible for giving a cancellation request for the subscriber data to

the old VLR once the acknowledgement for

the location update arrives from the new VLR. If, during location

updating, the new VLR

needs data from the old VLR, it is directly requested over the G

interface. Furthermore, the identity of subscriber or equipment can be

verified during a location update; for requesting and checking the

equipment identity, the MSC has an interface F to the EIR

For the connection of the different nodes in GSM network, different interface are defined

in GSM specifications which are discussed as below :-

Air Interface Or Um – Interface:-This interface is between the BTS (Base Transceiver

Station) and the MS (Mobile Station). To achieve a high spectral efficiency in a cellular

network a combination of :-

FDMA (Frequency Division Multiple Access)

TDMA (Time Division Multiple Access)

A Bis -- Interface :-The A Bis – interface is the interface between the BSC (Base Station

Controller) and the BTS. The interface companies traffic and control channels.

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A – Interface :-The a – Interface is the interface between the BSC and the MSC.

Logical Channels on the Um-Interface :-One or more logical channels may be

transmitted on physical channel. The different type of logical channel is determined by

the function of the information transmitted over it.The following types of logical channels

are defined :-

        Traffic channels

        Broadcast Channels

        Common Control Channels

        Dedicated Control Channels

The first channel type carries speech and data and the other types control information

(signaling).

The network attachment process consists of the following tasks :-

Cell Identification:-

When mobile station is switched on, it attempts to make contacts with a GSM PLMN by

performing the following tasks:-

Measure the BCCH channel

Search for a suitable cell

PLMN Selection :-

The particular PLMN to be contacted can be selected either in one of the following

modes:-  

        Automatic Mode

        Manual Mode

 Cell Selection:-

The mobile station attempts to find a suitable cell by passing throughthe list in descending

order of received signal strength

It should be cell of the selected PLMN

It should not be ‘barred’.

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The radio path laws between the MS and the selected

BTS must be below a  threshold set by the PLMN

operator.

It should not be in ‘ forbidden LA’s for roaming

No Suitable Cell Found:-

If the MS is unable to find a suitable cell to access, it attempts to access a cell irrespective

of the PLMN identity, and enters a ‘limited services’ state in which it can only attempt to

make emergency calls. 

7.1 GSM channels

The GSM physical layer, which resides on the first of the seven

layers of the Open

Systems Interconnection (OSI) Reference Model , contains very

complex functions. The physical channels are defined here by a TDMA

scheme. On top of the physical channels, a series of logical channels

are defined, which are transmitted in the time slots of the physical

channels. Logical channels perform a multiplicity of functions, such as

payload transport, signaling, broadcast of general system information,

synchronization and channel assignment.

Physical channels

Logical channels

7.1.1 Physical channel:

One timeslot of a TDMA-frame on one carrier is referred to as a physical

channel. There are 8 physical channels per carrier in GSM,channel 0-7(timeslot 0-7)

7.1.2 Logical channel:

A great variety of information must be transmitted between BTS and

the MS,for e.g. user data and control signaling.Depending on the kind of information

transmitted we refer to different logical channels.These logical channels are mapped on

physical channel. On Layer 1 of the OSI Reference Model, GSM defines a

series of logical channels, which are made available either in an

45

unassigned random access mode or in a dedicated mode assigned to a

specific user. Logical channels are divided into two categories

Ttraffic channel

Signaling (control) channels.

7.1.3 Traffic channels:

The Traffic Channels (TCHs) are used for the transmission of user

payload data (speech,data). They do not carry any control information

of Layer 3. Communication over a TCH can be circuit-switched or

packet-switched. In the circuit-switched case, the TCH provides a

transparent data connection or a connection that is specially treated

according to the carried service (e.g. telephony). For the packet-

switched mode, the TCH carries user data of OSI Layers 2 and 3

according to the recommendations of the X.25 standard or similar

standard packet protocols. A TCH may either be fully used (full-rate

TCH, TCH/F) or be split into two half-rate channels (half-rate TCH,

TCH/H), which can be allocated to different subscribers. Following ISDN

terminology, the GSM traffic channels are also designated as Bm

channel (mobile B channel) or Lm channel (lower-rate mobile channel,

with half the bit rate). A Bm channel is a TCH for the transmission of bit

streams of either 13 kbit/s of digitally coded speech or of data streams

at 14.5, 12, 6 or 3.6 kbit/s. Lm channels are TCH channels with less

transmission bandwidth than Bm channels and transport speech

signals of half the bit rate (TCH/H) or bit streams for data services with

6 or 3.6 kbit/s.

Group Channel Function Direction

Traffic channel TCH TCH/F, Bm

TCH/H, Lm

Full-rate TCH

Half-rate TCH

MS↔BSS

MS↔BSS

Signaling channels

(Dm)

BCH BCCH

FCCH

SCH

Broadcast control

Frequency correction

Synchronization

MS←BSS

MS←BSS

MS←BSS

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CCCH RACH

AGCH

PCH

NCH

DCCH SDCCH

SACCH

FACCH

Random access

Access grant

Paging

Notification

Stand-alone dedicated

control

Slow associated

control

Fast associated control

MS→BSS

MS←BSS

MS←BSS

MS←BSS

MS↔BSS

MS↔BSS

MS↔BSS

Table 7.2: Types of Logical Channels

7.1.4 Signaling channels:

The control and management of a cellular network demands a

very high signaling effort. Even when there is no active connection,

signaling information (for example, location update information) is

permanently transmitted over the air interface. The GSM signaling

channels offer a continuous, packet-oriented signaling service to MSs in

order to enable them to send and receive messages at any time over

the air interface to the BTS. Following ISDN terminology, the GSM

signaling channels are also called Dm channels (mobile D channel).

They are further divided into Broadcast Channel (BCH), Common

Control Channel (CCCH) and Dedicated Control Channel (DCCH).

The unidirectional BCHs are used by the BSS to broadcast the

same information to all MSs in a cell. The group of BCHs consists of

three channels.

7.1.4.1 Broadcast Control Channel (BCCH):

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On this channel, a series of information elements is broadcast to

the MSs which characterize the organization of the radio network, such

as radio channel configurations (of the currently used cell as well as of

the neighboring cells), synchronization information (frequencies as well

as frame numbering) and registration identifiers (LAI, CI, BSIC). In

particular, this includes information about the structural organization

(formats) of the CCCH of the local BTS. The BCCH is broadcast on the

first frequency assigned to the cell (the so-called BCCH carrier).

7.1.4.2 Frequency Correction Channel (FCCH):

On the FCCH, information about correction of the transmission

frequency is broadcast to the MSs (frequency correction burst).

7.1.4.3 Synchronization Channel (SCH):

The SCH broadcasts information to identify a BTS, i.e. BSIC. The

SCH also broadcasts data for the frame synchronization of a MS, i.e.

Reduced Frame Number (RFN) of the TDMA frame.

FCCH and SCH are only visible within protocol Layer 1, since they

are only needed for the operation of the radio subsystem. There is no

access to them from Layer 2. In spite of this fact, the SCH messages

contain data which are needed by Layer 3 for the administration of

radio resources. These two channels are always broadcast together

with the BCCH. The CCCH is a point-to-multipoint signaling channel to

deal with access management functions. This includes the assignment

of dedicated channels and paging to localize a MS. It comprises the

following.

7.1.4.4 Random Access Channel (RACH):

The RACH is the uplink portion of the CCCH.It is accessed from

the mobile stations in a cell without reservation in a competitive

multiple-access mode using the principle of slotted Aloha (Bertsekas

and Gallager,1987), to ask for a dedicated signaling channel for

exclusive use by one MS for one signaling transaction.

7.1.4.5 Access Grant Channel (AGCH):

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The AGCH is the downlink part of the CCCH. It is used to assign

an SDCCH or a TCH to a MS.

7.1.4.6 Paging Channel (PCH):

The PCH is also part of the downlink of the CCCH. It is used for

paging to find specific MSs. Notification Channel (NCH): The NCH is

used to inform MSs about incoming group and broadcast calls.

The last type of signaling channel, the DCCH is a bidirectional point-to-

point signaling

channel. An Associated Control Channel (ACCH) is also a dedicated

control channel, but it is assigned only in connection with a TCH or an

SDCCH. The group of Dedicated/Associated Control Channels (D/ACCH)

comprises the following.

7.1.4.7 Stand-alone Dedicated Control Channel (SDCCH):

The SDCCH is a dedicated point to-point signaling channel

(DCCH) which is not tied to the existence of a TCH (‘standalone’), i.e. it

is used for signaling between a MS and the BSS when there is no active

connection. The SDCCH is requested from the MS via the RACH and

assigned via the AGCH. After the completion of the signaling

transaction, the SDCCH is released and can be reassigned to

anotherMS. Examples of signaling transactions which use an SDCCH

are the updating of location information or parts of the connection

setup until the connection is switched through

7.1.4.8 Slow Associated Control Channel (SACCH):

An SACCH is always assigned and used with a TCH or an SDCCH.

The SACCH carries information for the optimal radio operation, e.g.,

commands for synchronization and transmitter power control and

reports on channel measurements (section 4.5). Data must be

transmitted continuously over the SACCH since the arrival of SACCH

packets is taken as proof of the existence of the physical radio

connection (section 4.5.3). When there is no signaling data to transmit,

the MS sends a measurement report with the current results of the

continuously conducted radio signal level measurements.

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7.1.4.9 Fast Associated Control Channel (FACCH):

By using dynamic preemptive multiplexing on a TCH, additional

bandwidth can be made available for signaling. The signaling channel

created this way is called FACCH. It is only assigned in connection with

a TCH, and its short-time usage goes at the expense of the user data

transport.

In addition to these channels, a Cell Broadcast Channel (CBCH) is

defined, which is

used to broadcast the messages of the Short Message Service Cell

Broadcast (SMSCB). The CBCH shares a physical channel with the

SDCCH.

7.2 RADIO RESOURCES MANAGEMENT:

This layer establishes link, both radio and fixed, between MS and MSC.

Main Functional Components :- MS, Base Station Subsystem, MSC.

RR layer concerns with the management of RR session. This session is initiated

by MS either for an outgoing call or in response to a paging message.

7.3 MOBILITY MANAGEMENT :

The Mobility management layer (MM) is built on top of the RR layer, and handles

the functions that arise from the mobility of the subscriber, as well as the authentication

and security aspects. Location management is concerned with the procedures that enables

the system to know the current location of a powered – on mobile station so that incoming

call routing can be completed.

7.4 LOCATION UPDATE:

A powered-on mobile is informed of an incoming call by a paging message sent

over the PAGCH channel of a cell. One extreme would be to page every cell in the

network for each call, which is obviously a waste of radio bandwidth. The other extreme

would be for the mobile to notify the system, via location updating messages, of its

current location at the individual cell level. This would require paging messages to be

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sent to exactly one cell, but would be very wasteful due to the large number of location

updating messages. A compromise solution used in GSM is to group cells into location

areas. Updating messages are required when moving between location areas, and mobile

stations are paged in the cells of their current location area.

The location updating procedures, and subsequent call routing, use the MSC and

two location registers: the Home Location Register (HLR) and the Visitor Location

Register (VLR). When a mobile station is switched on in a new location area, or it moves

to a new location area or different operator's PLMN, it must register with the network to

indicate its current location. In the normal case, a location update message is sent to the

new MSC/VLR, which records the location area information, and then sends the location

information to the subscriber's HLR. The information sent to the HLR is normally the

SS7 address of the new VLR, although it may be a routing number. The reason a routing

number is not normally assigned, even though it would reduce signaling, is that there is

only a limited number of routing numbers available in the new MSC/VLR and they are

allocated on demand for incoming calls. If the subscriber is entitled to service, the HLR

sends a subset of the subscriber information, needed for call control, to the new

MSC/VLR, and sends a message to the old MSC/VLR to cancel the old registration.

7.5 COMMUNICATION MANAGEMENT:

The Communication Management layer (CM) is responsible for Call Control

(CC), supplementary service management, and short message service management. Each

of these may be considered as a separate sub layer within the CM layer. Call control

attempts to follow the ISDN procedures specified in Q.931, although routing to a roaming

mobile subscriber is obviously unique to GSM. Other functions of the CC sub layer

include call establishment, selection of the type of service (including alternating between

services during a call), and call release.

7.6 CALL ROUTING:

Unlike routing in the fixed network, where a terminal is semi-permanently wired

to a central office, a GSM user can roam nationally and even internationally. The

directory number dialed to reach a mobile subscriber is called the Mobile Subscriber

ISDN (MSISDN), which is defined by the E.164 numbering plan. This number includes a

country code and a National Destination Code which identifies the subscriber's operator.

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The first few digits of the remaining subscriber number may identify the subscriber's

HLR within the home PLMN.

An incoming mobile terminating call is directed to the Gateway MSC (GMSC)

function. The GMSC is basically a switch, which is able to interrogate the subscriber's

HLR to obtain routing information, and thus contains a table linking MSISDNs to their

corresponding HLR. A simplification is to have a GSMC handle one specific PLMN. It

should be noted that the GMSC function is distinct from the MSC function, but is usually

implemented in an MSC.

The routing information that is returned to the GMSC is the Mobile Station

Roaming Number (MSRN), which is also defined by the E.164 numbering plan. MSRNs

are related to the geographical numbering plan, and not assigned to subscribers, nor are

they visible to subscribers.

The most general routing procedure begins with the GMSC querying the called

subscriber's HLR for an MSRN. The HLR typically stores only the SS7 address of the

subscriber's current VLR, and does not have the MSRN (see the location updating

section). The HLR must therefore query the subscriber's current VLR, which will

temporarily allocate an MSRN from its pool for the call. This MSRN is returned to the

HLR and back to the GMSC, which can then route the call to the new MSC. At the new

MSC, the IMSI corresponding to the MSRN is looked up, and the mobile is paged in its

current location area.

7.7 Call Processing And SMS:

Mobile originated (MO) call: - There are four types of distinct phase

Setup phase Ringing phase Conversation phase Release phase

Setup phase is the most important phase and includes

Authentication of the subscriber

Ciphering of data over radio interface

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Validation of mobile equipment

Validation of subscriber data at VLR for requests service

Assignment of a voice channel

The MS hears the ringing tone from the destination local exchange through the

establishment voice path.

7.8 MOBILE CALL SETUP:

Mobile call setup involves exchange of no. of message between the various elements in

the system. For setting up a mobile call following process is involved. It deals with two

examples: -

Terminating call when the MS is in the HPLMN.

Terminating call when the MS is roaming.

Figure 7.3: Depicts the different network elements involved in the call setup

The call set up broadly involves the following steps: -

PSTN subscriber dials MSISDN

Call is routed by PSTN network to GMSC of HPLMN of the dialed mobile

subscriber.

GMSC interrogates HLR for verification of the access privileges profile and for

obtaining the location details if the call is permitted.

HLR directs the call to VLR of MSC area in which the mobile customer is

currently located.

MSC interrogates VLR to obtain exact location of the MS.

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VLR provides LAC to the MSC.

MSC translates the LAC code into BTS identity.

BSS pages all the BTSs identified by MSC within which MS is located using

IMSI .

MS responds to the paging

Call is connected .

In case of roaming call MS will be located in a VPLMN

In such case steps are as follows:

On registration with VPLMN ,HLR will place a pointer in the data base for MS

indicating the current VLR address.

On interrogation by GMSC of the HPLMN ,HLR will in turn interrogate VLR of

VPLMN using the already stored pointer

VLR in VPLMN will assign a roaming number called in MSRN . To enable the

HPLMN to route the call to the VPLMN

Using MSRN , call is routed back from HPLMN to VPLMN and VMSC

interrogates the VLR

VLR provides the LAC and call proceeds exactly in the same manner as for the

call in.

7.9 PERFORMANCE ENHANCEMENT TECHNIQUES

GSM System incorporates a number of performance enhancement techniques to

ensure excellent quality of service under different load and transmission environment. 

Some of the important techniques as given below:

Discontinuous Transmission (DTX)

Discontinuous Reception (RTX)

Frequency Hopping (FH)

Power Control (PC)

Discontinuous Transmission (DTX) is a technique that improves the

performance of the system from the point of view of quality as well as capacity.  The

concept of DTX is based on the fact that speech activity in any voice connection exists

only fro 40% of time.  Rest of the 60% time, the channel carries “silence”.  DTX

attempts  to de-assign the channels from an active connection during such “silence”

54

period and assigns them to needy subscribers.  Speech channels are reassigned to the

subscribers the moment they resume the speech activity.  Thus a given number of voice

channels can be used to cater to more number of simultaneous conversations resulting in

increased capacity of the system.  DTX, however, would need a mechanism to detect

Voice activity with precision.  Failure to discriminate between voice activity and

background noise would result in annoying clicks and would render the DTX inefficient. 

It is also required to generate Comfort Noise at receiver to avoid the feeling of the

originating set being dead.

DTX can also be used a mechanism  to improve the quality of the connection by

controlling the “crowd” in the air.  The interference in RF channels increase with the

traffic load and DTX under such situation brings down the load on the RF thereby

improving the quality of the connection.  Since signal transmission is avoided during

inactive period, DTX also saves the battery power in the mobile handset. 

Like DTX, Discontinuous Reception (RTX) is another technique used to conserve

mobile station’s battery power.  This is achieved by assigning specific time slot to each

mobile station to watch for paging on incoming call.  The MS listen to the paging channel

during the specified time slot only and go to sleep until the occurrence of next time slot. 

Thus, between two time slots, the MS consumes   very little power as it remains in sleep

mode during the intervening period. 

Frequency Hopping (FH) is a technique to randomize the interference across the

active mobiles by constantly changing RF channel for each of the connection during the

conversation.  This will prevent a interference prone RF channel being assigned to a

customer for the whole period of his connection thereby increasing the quality of the

speech. 

Power Control (PC) is another performance enhance techniques aimed at both

saving the power of the battery in the MS as well as to regulate the power transmitted in

the air to levels just sufficient to ensure appropriate speech quality.  The BTS performs

the measurement of the power level of each MS and sends Power control commands to

adjust the transmit power level of each mobile station so as to ensure that BTS receives

signals of just the right power. 

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There are a number of other performance and capacity improvement technioques

that are quite complicated and are beyond the scope of this article.

8. GSM - Security and Encryption

The security methods standardized for the GSM System make it the most secure

cellular telecommunications standard currently available. Although the confidentiality of

a call and anonymity of the GSM subscriber is only guaranteed on the radio channel, this

is a major step in achieving end-to- end security.

The subscriber's anonymity is ensured through the use of temporary identification

numbers. The confidentiality of the communication itself on the radio link is performed

by the application of encryption algorithms and frequency hopping which could only be

realized using digital systems and signaling.

The security measures implemented for GSM subscribers.

8.1 Mobile Station Authentication:

The GSM network authenticates the identity of the subscriber through the use of a

challenge-response mechanism. A 128-bit random number (RAND) is sent to the MS.

The MS computes the 32-bit signed response (SRES) based on the encryption of the

random number (RAND) with the authentication algorithm (A3) using the individual

subscriber authentication key (Ki). Upon receiving the signed response (SRES) from the

subscriber, the GSM network repeats the calculation to verify the identity of the

subscriber.

Note that the individual subscriber authentication key (Ki) is never transmitted over the

radio channel. It is present in the subscriber's SIM, as well as the AUC, HLR, and VLR

databases as previously described. If the received SRES agrees with the calculated value,

the MS has been successfully authenticated and may continue. If the values do not match,

the connection is terminated and an authentication failure indicated to the MS.

The calculation of the signed response is processed within the SIM. This provides

enhanced security, because the confidential subscriber information such as the IMSI or

56

the individual subscriber authentication key (Ki) is never released from the SIM during

the authentication process.

8.2 Signaling and Data Confidentiality:

The SIM contains the ciphering key generating algorithm (A8) which is used to produce

the 64-bit ciphering key (Kc). The ciphering key is computed by applying the same

random number (RAND) used in the authentication process to the ciphering key

generating algorithm (A8) with the individual subscriber authentication key (Ki). As will

be shown in later sections, the ciphering key (Kc) is used to encrypt and decrypt the data

between the MS and BS.

An additional level of security is provided by having the means to change the ciphering

key, making the system more resistant to eavesdropping. The ciphering key may be

changed at regular intervals as required by network design and security considerations. In

a similar manner to the authentication process, the computation of the ciphering key (Kc)

takes place internally within the SIM. Therefore sensitive information such as the

individual subscriber authentication key (Ki) is never revealed by the SIM.

Encrypted voice and data communications between the MS and the network is

accomplished through use of the ciphering algorithm A5. Encrypted communication is

initiated by a ciphering mode request command from the GSM network. Upon receipt of

this command, the mobile station begins encryption and decryption of data using the

ciphering algorithm (A5) and the ciphering key (Kc).

8.3 Subscriber Identity Confidentiality:

To ensure subscriber identity confidentiality, the Temporary Mobile Subscriber Identity

(TMSI) is used. The TMSI is sent to the mobile station after the authentication and

encryption procedures have taken place. The mobile station responds by confirming

reception of the TMSI. The TMSI is valid in the location area in which it was issued. For

communications outside the location area, the Location Area Identification (LAI) is

necessary in addition to the TMSI.

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9. GSM APPLICATIONS,ADVANTAGES AND FUTURE

9.1 GSM APPLICATIONS

Mobile telephony

GSM-R

Telemetry System

Fleet management

Automatic meter reading

Toll Collection

Remote control and fault reporting of DG sets

Value Added Services

Access control devices: Now access control devices can communicate with

servers and security staff through SMS messaging. Complete log of transaction is

available at the head-office Server instantly without any wiring involved and

device can instantly alert security personnel on their mobile phone in case of any

problem. Some companies are introducing this technology in all Fingerprint

Access control and time attendance products. You can achive high security any

reliability.

Transaction terminals: EDC machines, POS terminals can use SMS messaging

to confirm transactions from central servers. The main benefit is that central

server can be anywhere in the world. Today you need local servers in every city

with multiple telephone lines. You save huge infrastructure costs as well as per

transaction cost.

Supply Chain Management: Today SCM require huge IT infrastructure with

leased lines, networking devices, data centre, workstations and still you have large

58

downtimes and high costs. You can do all this at a fraction of the cost with GSM

M2M technology. A central server in your head office with GSM capability is the

answer, you can receive instant transaction data from all your branch offices,

warehouses and business associates with nil downtime and low cost.

9.2 Advantages

Extensive Coverage

The most obvious advantage of GSM is its widespread use throughout the world.

According to Gsmworld.com, GSM has a harmonized spectrum, which means that even

though different countries may operate on different frequency bands, users can transfer

seamlessly between networks and keep the same number. As a result, GSM users

essentially have coverage in over 218 countries.

Greater Phone Variety

Another advantage of GSM is that because it is used throughout the world, there is

a greater variety of phones that operate on GSM. Therefore, consumers have more

flexibility in choosing a handset that fits their specific desires, and they are not limited to

purchasing phones only made in their respective country.

No Roaming Charges on International Calls

Because GSM is the same network worldwide, users are not charged a roaming

fee for international calls. However, most providers still charge a service fee on

international calls.

Short Data Size

You data size per transaction should be small like 1-3 lines. e.g. banking

transaction data, sales/purchase data, consignment tracking data, updates. These small but

important transaction data can be sent through SMS messaging which cost even less then

a local telephone call or sometimes free of cost worldwide. Hence with negligible cost

you are able to send critical information to your head office located anywhere in the

59

world from multiple points. You can also transfer faxes, large data through GSM but this

will be as or more costly compared to landline networks.

Multiple Remote Data Collection Points

If you have multiple data collections points situated all over your city, state,

country or worldwide you will benefit the most. The data can be sent from multiple points

like your branch offices, business associates, warehouses, agents with devices like GSM

modems connected to PCs, GSM electronic terminals and Mobile phones. Many a times

some places like warehouses may be situated at remote location may not have landline or

internet but you will have GSM network still available easily.

High Uptime

If your business require high uptime and availability GSM is best suitable for you

as GSM mobile networks have high uptime compared to landline, internet and other

communication mediums. Also in situations where you expect that someone may

sabotage your communication systems by cutting wires or taping landlines, you can

depend on GSM wireless communication.

Large Transaction Volumes

GSM SMS messaging can handle large number of transaction in a very short

time. You can receive large number SMS messages on your server like e-mails without

internet connectivity. E-mails normally get delayed a lot but SMS messages are almost

instantaneous for instant transactions. consider situation like shop owners doing credit

card transaction with GSM technology instead of conventional landlines. many a time

you find local transaction servers busy as these servers use multiple telephone lines to

take care of multiple transactions, whereas one GSM connection is enough to handle

hundreds of transaction per minute.

Mobility, Quick installation

GSM technology allow mobility, GSM terminals, modems can be just picked and

installed at other location unlike telephone lines. Also you can be mobile with GSM

terminals and can also communicate with server using your mobile phone. You can just

60

purchase the GSM hardware like modems, terminals and mobile handsets, insert SIM

cards, configure software and your are ready for GSM communication. GSM solutions

can be implemented within few weeks whereas it may take many months to implement

the infrastructure for other technologies.

9.2.1 Advantages of GSM over Analog system

• Capacity increases

• Reduced RF transmission power and longer battery life.

• International roaming capability.

• Better security against fraud (through terminal validation and user authentication).

• Encryption capability for information security and privacy.

• Compatibility with ISDN,leading to wider range of services.

9.2.2 Disadvantages

Bandwidth Lag

Perhaps the greatest disadvantage of GSM is that multiple users share the same

bandwidth. With enough users, the transmission can encounter interference. Therefore,

faster technologies, such as 3G, have been developed on different types of networks than

GSM, such as CDMA, in order to avoid such bandwidth limitations.

Causes Electronic Interference

Another disadvantage of GSM is that is can interfere with certain electronics, such

as pace makers and hearing aids, according to Inc.Technology. com. Such interference is

due to the fact that GSM uses a pulse-transmission technology. As a result, many

locations such as hospitals and airplanes require cell phones to be turned off.

Dropped and Missed Calls

According to Cellular News, call quality problems, including dropped calls and

missed calls are common problems with GSM technology. These problems result directly

from the technology in use. GSM technology cannot accommodate as many callers on a

single cell tower as the more modern CDMA technology. This means that callers in areas

61

where there are not a preponderance of cell towers may find that the call problems on

GSM will be more common.

Security Issues

ZDNet UK reports that GSM has a serious security flaw, demonstrated by a

hacker who was able to intercept phone calls from a number of GSM-based cellular

phones. The problem is based directly on the technology according to this hacker and his

solution was to "turn off" the GSM technology (only the older 2G technology though)

that is commonly used by people all over the world. The problem is largely mitigated

however by the use of the more modern 3G technology that is commonly used (as of

November, 2010) on many GSM phones.

Efficiency

Another problem with GSM is a network problem rather than a consumer

problem, though it is a consumer problem for those who don't want to see a proliferation

of cellular towers. As previously noted, GSM technology can handle fewer callers on a

single cellular tower. Therefore, networks who work with GSM must find ever more

areas to built GSM cellular towers, causing them to have problems with costs and

locations. By the same token, some consumers who prefer not to see a proliferation of

cellular towers consider this a problem because the cellular towers must be placed in

more and more urban areas, potentially spreading more radiation and causing what some

consider a blight on the landscape.

9.3 Future Of GSM

2nd Generation

o D-AMPS- .9.6 Kbps to 14.4 Kbps

o GSM -9.6 Kbps (data rate)

2.5 Generation ( Future of GSM)

o HSCSD (High Speed ckt Switched data)

Data rate : 76.8 Kbps (9.6 x 8 kbps)

o GPRS (General Packet Radio service)

Data rate: 14.4 - 115.2 Kbps

o EDGE (Enhanced data rate for GSM Evolution)

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Data rate: 547.2 Kbps (max)

3 Generationo UMTS

Data rate: 2+ Mbps, up to 384 Kbpso CDMA2000

Data rate: 614 Kbps

o WCDMA(Wide band CDMA)

Data rate : 384 Kbps (wide area access), 2 Mbps

(local area access)

10.CONCLUSION

The GSM system, and its sibling systems operating at 1.8 GHz (called DCS1800)

and 1.9 GHz (called GSM1900 or PCS1900, and operating in North America), are a first

approach at a true personal communication system. The SIM card is a novel approach that

implements personal mobility in addition to terminal mobility. Together with

international roaming, and support for a variety of services such as telephony, data

transfer, fax, Short Message Service, and supplementary services, GSM comes close to

fulfilling the requirements for a personal communication system: close enough that it is

being used as a basis for the next generation of mobile communication technology in

Europe, the Universal Mobile Telecommunication System (UMTS).

GSM is a very complex standard, but that is probably the price that must be paid

to achieve the level of integrated service and quality offered while subject to the rather

severe restrictions imposed by the radio environment.

Thus we have studied functionality of seamless global roaming in GSM

Architecture. In call processing we were taught about call origination and call

termination. Also we learned various new feature and services provided by the third

generation.

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11. BIBLIOGRAPHY

1. 1. Communication Systems - George Kennedy

2. 2. GSM – Architecture, Protocols and Services -Jörg Eberspächer, Christian

Hartmann

3. The GSM system for mobile communication  -Mouly & Marie-bernadette Pautet

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